The present invention relates to a method of and to an apparatus for changing bobbins in machines wherein webs of convoluted wrapping or other material are processed continuously so that the machines must or should receive a continuous web of flexible strip material. Typical examples of machines which process continuous webs of wrapping or other material are cigarette rod making machines wherein the web forms the tubular wrapper of a continuous cigarette rod, filter rod making machines wherein the web forms the tubular wrapper of a continuous filter rod, and cigarette packing machines wherein arrays of cigarettes are draped into blanks to form cigarette packs or cartons of cigarette packs. In such machines, the webs must be fed at a high speed and without interruptions because any, even short, interruptions can entail huge losses in output. By way of example, a modern cigarette maker can turn out up to and in excess of 8000 cigarettes per minute so that a one-minute interruption results in a loss of approximately 40 cartons of cigarette packs.
One mode of maintaining a bobbin in proper position for unwinding is to mount the bobbin on a mandrel which extends through the hollow core of the bobbin. Another conventional mode of holding a bobbin in a position for unwinding is to force a rod through the core so that the rod is a tight fit in the core, and to place the end portions of the rod into a rack wherein the rod rotates with the bobbin in response to unwinding of the web. In accordance with a further proposal, the bobbin which is in the process of paying out the web is held by rollers which engage its periphery (i.e., the outermost convolution of the supply of web on the core). East German Pat. No. 43,784 discloses an apparatus wherein the bobbin which is about to pay out its web is placed onto a set of rollers and is held thereon for the purpose to prepare the leader of its web for slicing to the trailing end of the running web. The thus prepared bobbin is transferred to the unwinding station where two mandrels extend into its core from opposite axial ends in the course of the web unwinding operation.
A further mode of maintaining a bobbin in a position of readiness for unwinding of its web is disclosed in German Utility Model No. 1 888 719. The periphery of the bobbin is engaged by supporting rollers and the core of the freshly expired bobbin is expelled from the unwinding station in response to short-lasting retraction of one of the rollers. A lever is used to transfer a fresh bobbin from a position of readiness into the unwinding station.
Still another apparatus for supporting a bobbin in the course of the unwinding operation is disclosed in commonly owned U.S. Pat. No. 3,279,717 to Schubert. This apparatus is particularly suited for manipulation of bobbins which carry supplies of thin or very thin web- or strip-shaped material, such as cigarette paper. The bobbin at the unwinding station is supported by a belt conveyor which is driven at a speed slightly less than the speed of the withdrawing rolls so as to maintain the web under tension.
All of the above described conventional apparatus exhibit one or more drawbacks, particularly as concerns the possibility of automating the bobbin changing operation which is desirable in modern production lines serving to turn out large quantities of goods which are draped into or contain a flexible web or strip material containing or consisting of paper, metallic foil, plastic foil or the like.